1. Field of Invention
The invention relates an ink ribbon cartridge and, more particularly, to an attachable/detachable ink ribbon cartridge.
2. Description of Related Art
Image forming devices, such as, printers and facsimile machines, which print images/data via a thermal transfer method generally employ an ink ribbon to form an image on an image recording medium. The ink ribbon is typically held by an ink ribbon cartridge that is detachably arranged in the image forming device. An ink ribbon cartridge generally includes a supply shaft, a take-up shaft and a cartridge frame. The supply shaft maintains thereon the unused portion of an ink ribbon sheet and generally, an unused portion of the ink ribbon sheet is maintained in the form of a roll thereon. The take-up shaft maintains thereon the used portion of the ink ribbon sheet and generally, the used portion of the ink ribbon sheet is maintained in the form of a roll thereon. To print an image on an image recording medium, the ink ribbon sheet, supplied by (e.g., rolled out from) the supply shaft, is overlapped with the recording medium (e.g., paper) and heated by a thermal head. The heat causes the color elements on the ink ribbon to be transferred to the image recording medium. The used portion of the ink ribbon is then taken up by (e.g., rolled onto) the take-up shaft.
One way to improve the quality of the image produced using such a thermal transfer method, is to subject the ink ribbon sheet to a sufficient amount of tension such that the portion of the ink ribbon sheet extending from the supply shaft to the take-up shaft is not loose and/or wrinkled to enable corresponding unwrinkled/stretched portions of the ink ribbon and the recording medium to consistently overlap each other. If the ink ribbon sheet is loose and/or wrinkled, for example, the color elements from the ink ribbon sheet may not be properly transferred to the image recording medium because some of the ink components may not be transferred to the recording medium at all and/or some of the ink components may be transferred to improper areas of the recording medium. In such a case, portions of the image may, for example, be smudged, missing, shifted, lighter, darker, etc. and thus, the quality of the formed image is sacrificed. One way to reduce, and preferably completely prevent, the loosening and/or wrinkling of the ink ribbon sheet is to apply a tension to the supply shaft in order to prevent over-rotation of the supply shaft in a direction which releases some of the ink ribbon sheet.
To reduce the occurrence of a loose or wrinkled ink ribbon sheet, JP 2001-130075 discloses a back tension mechanism which supplies a predetermined rotation resistance to the supply shaft of an ink ribbon cartridge. The back tension mechanism disclosed therein utilizes a resin spool, which is rotatably mounted on an end of the supply shaft, and a spring, which presses the resin spool against the resin cartridge frame. When a surface of the resin cartridge rubs against a surface of the resin supply spool, a frictional force is generated therebetween. Accordingly, a back tension (i.e., rotation resistance) is applied against the rotation of the resin spool with the unused ink ribbon thereon (i.e., against the release of the ink ribbon on the resin supply spool). The applied back tension helps keep the ink ribbon from rotating excessively (i.e., supplying more ink ribbon than needed) and thereby loosening and/or wrinkling thereof.
The back tension mechanism employed in JP 2001-130075, however, depends on the frictional force generated between a surface of the resin supply spool and a surface of the resin cartridge frame (i.e., two resin surfaces). The magnitude of the frictional force between two resin members is dependent on changes in the environment and thus, the magnitude of the frictional force between the surface of the resin supply spool and the corresponding surface of the resin cartridge frame may change based the surrounding temperature, for example. Thus, a consistent amount of back tension may not be applied to the supply spool because the tension applied to the resin supply spool is dependent, for example, on the surrounding temperature of the image forming apparatus employing such an ink ribbon cartridge. Therefore, due to environmental differences, the generated frictional force may not be consistently substantially equal to an intended predetermined amount. In such a case, the frictional force generated may not be sufficient to apply the necessary back tension against the rotation of the supply shaft and the quality of images being formed may be hindered as a result of a wrinkled/loose ink ribbon sheet.
JP 9-109524 discloses another back tension mechanism for a supply shaft of an ink ribbon cartridge. The back tension mechanism disclosed therein employs a felt member arranged between a disk portion and a round flat plate. A spring urges the disk portion against the felt member and the round flat plate, and a back tension is applied to the ink ribbon sheet by a frictional force generated between corresponding surfaces of the felt member and the disk portion. In the mechanism disclosed therein, the spring and the round flat plate, for example, are provided on an external circumference of the revolving shaft and are part of the printer. The spring is provided between a surface of the gear and a first surface of the disk portion, and one surface of the felt member is secured the round flat plate while the other surface of the felt member is urged by the spring to be in contact with the second surface of the disk portion. Thus, to employ the back tension mechanism disclosed therein, a space for at least the spring and the round flat plate of the back tension mechanism must be allocated in the main body of the printing device. Accordingly, a size of the image forming apparatus employing the back tension mechanism disclosed in JP 9-109524 may need to be increased in order to accommodate for the components of the back tension. Further, as a result of wear and tear, the felt member may, for example, deteriorate and the generated resistance may not be in substantially equal to the predetermined desired rotation resistance. However, in the back tension mechanism disclosed herein the back tension mechanism is secured (i.e., screwed) to the printer. Thus, if for example, the felt member needs to be replaced, disassembly of the back tension mechanism from the printer is required.
Another way to improve an attachable/detachable ink cartridge is to provide an ink cartridge frame which allows for easier handling and attachment/detachment thereof to/from the image forming device. Generally, as disclosed, for example, in JP 2003-182130, ink cartridges employ a structure in which the ink ribbon supporting shafts are rotatably connected by a frame member. The frame member disclosed in JP 2003-182130 employs a pair of side frame members, which are independent of each other. The right ends of the ink ribbon shafts are supported by support members which are rotatably attached to the right side frame and the left ends of the ink ribbon shafts are supported by support members which are rotatably attached to the left side frame. Further, all the support members are attachable to and detachable from the side frame members.
Attachment and detachment of such an ink cartridge can be difficult and time consuming because it is necessary to correctly install all the attachable/detachable components of the ink cartridge and, in some circumstances, for example, while assembling one group of attachable/detachable components another group of attachable/detachable components detach from the frame. Also, an ink cartridge having a frame consisting solely of two side members can be wobbly and unstable, making handling and attachment and detachment thereof more difficult.
Another way to improve an ink cartridge is to provide an ink cartridge that is an attachable/detachable ink cartridge having components which maintain their connection with corresponding components during attachment and detachment of the ink cartridge and/or during replacement of the ink ribbon sheet. An example of a known supporting member 100 is illustrated in FIG. 23. The known supporting member 100 includes a gear member 102, which is equipped with a drive gear 101 and a spool member 103. One end of the spool portion is inserted into a receiving portion of the take-up rotating shaft body and the other end of the spool portion has elastic pieces 104 projecting therefrom. The gear member 102 has engaging holes which receive the elastic pieces 104 of the spool portion. Engaging protrusions 104a on the elastic pieces 104 engage with the engaging holes 105 and the spool member and the gear member are thereby connected. However, when such a structure is tilted, due to an external force applied from a side of the spool member 103, such as, for example, during removal of a shaft to which it is connected, the elastic piece 104 receives a force which separates the elastic piece from the engaging hole 105. Therefore, in such a structure, the spool member 103 and the gear member are too easily separated.